Miniaturized ferrite phase shifters for electronically steered antenna arrays

ABSTRACT

DESCRIBED ARE MINIATURIZED ANALOG X-BAND MICROSTRIP FERRITE PHASE SHIFTERS PARTICULARLY ADAPTED FOR USE IN AIRBORNE ANTENNA ARRAYS. ALSO DESCRIBED IS A NOVEL ANTENNA ARRAY ASSEMBLY ITSELF. THE ELEMENTS CONTAINING THE PHASE SHIFTERS ARE DESIGNED INTO HALF-WAVELENGTH SPACING TO ACHIEVE A TWO-AXIS SCAN AND COMPRISE MICROSTRIP TRANSMISSION LINES DEPOSITED ON THIN FERRITE FILMS SURROUNDED BY SUITABLE ACTUATING COILS.

United States Patent [72] Inventor Daniel C. Buck Hanover, Md.

[2|] Appl. No. 842,653

[22] Filed July 17, I969 [45] Patented [73] Assignee June 28, I971 Westinghouse Electric Corporation Pittsburgh, Pa.

[54] MINIATURIZED FERRITE PHASE SHIFIERS FOR ELECTRONICALLY STEERED ANTENNA ARRAYS 9 Claims, 7 Drawing Figs.

[52] US. Cl 343/741, 333/26, 333/31, 333/84, 343/8 l 6, 343/854 [51] lnt.Cl.....- H03l17/36, HOIp 3/08, HOlg 3/26 [50] Field of Search 343/741,

. [56] References Cited UNITED STATES PATENTS 3,289,115 10/1966 Carr 333/31 3,377,592 4/1968 Robieux etal OTHER REFERENCES DEVELOPMENTS IN PRINTED ANTENNA DESIGN McDonough, Malech and Kowalsky in Electronic Design" June 1, I957; pages 42- 45 Primary Examiner-Herman Karl Saalbach Assistant Examiner-Marvin Nussbaum Attorneys-F. H. Henson and E. P. Klipfel ABSTRACT: Described are miniaturized analog X-band microstrip ferrite phase shifters particularly adapted for use in airborne antenna arrays. Also described is a novel antenna array assembly itself. The elements containing the phase shifters are designed into half-wavelength spacing to achieve a two-axis scan and comprise microstrip transmission lines deposited on thin ferrite films surrounded by suitable actuating coils.

PATEN'IEI] JUN 2 8 197:

SHEET 1 BF 2 FIG. 2.

FIG. 3.

COIL

RECEIVE INVENTOR. DAN/EL c. BUCK 61%? W TRANSM/ MINKATURIZED FERRITEE PHASE SHIFTERS FOR ELECTRONICALLY STEERED ANTENNA ARRAYS CROSS-REFERENCES TO RELATED APPLICATIONS None.

BACKGROUND OF THE INVENTION The present invention is particularly adapted for use in applications such as antenna systems employing a plurality of radiating elements which are electronically scanned. That is, by varying the phases of the respective signals fed to the individual radiating elements, the composite radiated beam can be caused to scan back and forth without mechanical movement of the antenna itself.

Such electrically steerable antenna arrays have been made using diode or ferrite phase shifters, but generally have been limited to applications in which the beam is steered in a stepwise or digital manner. In certain types of radar installations such as pulse doppler radar, however, step scanning imposes severe limitations on performance. Accordingly, a means for providing a continuously scanning beam is highly desirable for such applications. Diode phase shifters can be ruled out for continuous scanners since the diodes are basically used as switches rather than as variable reactances. On the other hand, ferrite phase shifters can be utilized to effect an analog variation in phase shift. Such devices ordinarily take the form of Reggia-Spencer phase shifters as described, for example, in Proceedings of the IRE, Vol. 45, pages 1510-1517, Nov. 1957, latching nonreciprocal phase shifters or coaxial ferrite phase shifters. None of these types as represented by the present state-of-the-art meet the requirements of a small cross section miniaturized phase shifter. Latching nonreciprocal ferrite phase shifters can be ruled out as impractical due to their nonreciprocal feature requiring the antenna system to be switched between transmit and receive. Present state-oftheart antennas require that transmitted and received signals be processed simultaneously. The cross section of the Reggia- Spencer phase shifter is characterized by wave guide dimensions much too large for one-half wavelength spacing in two dimensions and, accordingly, cannot be used for a two-axis scan. Previous coaxial phase shifters are typified by operation from L-band through C-band. These phase shifters are largely designed to operate with magnetic bias fields greater than gyromagnetic resonance. While this mode of operation is useful in meeting very high peak power requirements, it leads to an unacceptably high drive power and excessive weight in airborne phased arrays consisting of several hundred to a few thousand phase shifters. Furthermore, for very large arrays, individual phase shifters need to handle only a few watts even though the aperture power is several kilowatts.

SUMMARY OF THE INVENTION As an overall object, the present invention seeks to provide a low cost phase shifter, particularly adapted for airborne twoaxis scan antenna arrays, which has low insertion losses, is light in weight, small in size, and has low core losses.

More specifically, an object of the invention is to provide a phase shifter of the type described comprising a microstrip conductor deposited on one side of a ferrite slab, the other side of the slab being coated with a layer of metal to form a ground plane. With such an arrangement, it is possible to form, on the same ferrite slab, antenna elements, circulators, and other miniaturized microstrip transmission components without the need for bulky wave guide components.

Still another object of the invention is to provide a unique antenna array comprising a plurality of ferrite phase shifters spaced one-half wavelength apart to achieve two-axis scanning.

In accordance with the invention, a ferrite phase shifter for electromagnetic wave energy is provided comprising a slab or deposit of ferrite material having a ground plane deposited on one side thereof and a microstrip conductor deposited on the other side. An electromagnetic coil surrounds the ferrite slab and is adapted to produce a longitudinal magnetic field extending parallel to the direction of wave propagation along the microstrip conductor; while microstrips are deposited on one end of the ferrite slab and connected to the first-mentioned microstrip to form an antenna element. This antenna element, preferably formed by vapor deposition techniques, may be either a loop antenna or a dipole antenna and may be formed on one side of the ferrite slab or both sides. That is, by connecting one side of a dipole antenna directly to the microstrip conductor and the other side to the microstrip conductor through a Balun'loop circuit, the wave energy in one-half of the dipole antenna will be out of phase with that in the other half. Alternatively, one part of the dipole antenna can be formed on the top of the ferrite slab and connected to the microstrip conductor while the other half can be formed on the bottom and connected to the metal film forming the ground plane.

The end of the microstrip conductor opposite the antenna can be connected directly to a wave energy distribution system or can be provided with a dipole antenna itself such that all elements in an antenna array can be space fed from a feed horn or the like.

Further, in accordance with the invention, a plurality of ferrite phase shifters of the type described above are supported on a pair of spaced plates forming an antenna reflector. These spaced plates, in turn, are connected to the ground planes of the respective ferrite phase shifters. A source of 8+ potential can be connected to one side of all of the coils surrounding the ferrite phase shifters, while the opposite ends of the coils can be connected through individual transistor drivers and control wires to external control circuitry.

The above and other objects and features of the invention will become apparent from the following detailed description taken in connection with the accompanying drawings which form a part of this specification, and in which:

FIG. 1 is a perspective view of a generalized configuration of the ferrite phase shifter of the invention;

FIG. 2 is a schematic illustration of one type of ferrite phase shifter constructed in accordance with the teachings of the invention and incorporating an integral antenna element;

FIG. 3 is a schematic illustration of still another type of phase shifter constructed in accordance with the teachings of the invention and provided at one end with a loop antenna and at the other end with a circulator;

FIG. 4 illustrates a type of dipole antenna configuration which can be deposited on one end of the ferrite slab of the phase shifter of the invention on opposite sides thereof;

FIG. 5 is a schematic illustration of still another embodiment of the invention having dipole antennas at opposite ends of the ferrite phase shifter and adapted for use in space feed arrangements;

FIG. 6 is an illustration of a typical antenna array employing a space feed system; and

FIG. 7 is a cross-sectional view of the antenna construction of FIG. 6.

With reference now to the drawings, and particularly to FIG. I, the phase shifter shown includes a slab 10 of ferrite material having a microstrip conductor 12 deposited on one side thereof as, for example, by vapor deposition techniques. The microstrip 12 may be formed, as an example, from copper. On the other side of the'ferrite slab 10 is a layer 14 of metal forming a ground plane. The slab 10 with the conductor 12 and ground plane 14 deposited thereon is carried within an outer metallic casing 16 surrounded by means of an electromagnetic coil 18 adapted to produce an applied magnetic field H, extending along the axis of the microstrip conductor.

If it is assumed, for example, that the center conductor of a coaxial transmission line is connected to the microstrip conductor I2 and the outer cylindrical conductor connected to ground plane M, wave energy will travel along the ferrite phase shifter with the electric field extending between the microstrip conductor 12 and the ground plane M in a direction transverse to the direction of wave propagation.

Likewise, the microwave frequency magnetic field 41, will surround the microstrip conductor 12 and be transverse to the direction of wave propagation. In this respect, the mode of wave propagation is quasi-TEM. When an external magnetic field, H is applied along the axis of the phase shifter by means of the coil 1%, the wave energy passing through the phase shifter will be shifted in phase, the amount of the phase shift being dependent upon the magnitude of the applied magnetic field. Furthermore, the device is reciprocal in nature. That is, it can shift the phase of wave energy the same amount for either direction of propagation.

For maximum phase shift in a single-line microstrip phase shifter such as that shown in FIG. I, the line itself must be long. A typical length at X-band is inches using a magnesium-manganese ferrite with Vii-inch square cross section. This shape is long and needle-shaped, a geometry which looks magnetically like a section of a thin toroid of infinite diameter. Thus, when the device is magnetized to saturation, there will be a residual differential phase associated with the residual magnetization in the needlelike ferrite body.

The disadvantages of the single-line arrangement of FIG. H can be overcome by the meander line version shown in FIGS. 2 and 3. In FIG. 2, for example, a microstrip transmission line 20 is folded into a meander line 22 before it passes to a dipole antenna 24. The meander line version of FIG. 2 has the advantage of a smaller, surrounding actuating coil 26, due to the fact that the meander line is folded into a smaller length. Furthermore, the meander line geometry shown in FIG. 2 has virtually zero residual phase due to the fact that in the central region of the ferrite the residual magnetization is nearly zero, the flux lines associated with the poles at the end of the sample being largely external to the ferrite near its center. Experiments have shown that a 1000 meander line phase shifter at C-band has less than of residual phase.

In the embodiment shown in FIG. 2, the right end of the meander line 22 is connected to one element 28 of the dipole antenna 24. The other element 30 of the dipole antenna is connected through a Balurl loop or circuit 32 to the same microstrip conductor whereby the wave energy in element of the dipole antenna will be 180' out of phase with respect to that in element 28. As will be understood, the microstrip conductor 20 is again deposited on a ferrite slab 34 having provided on its undersurface a ground plane, not shown.

In FIG. 3, the embodiment of the invention is similar to that shown in FIG. 2 and, accordingly, elements in FIG. 3 which correspond to those shown in FIG. 2 are identified by like reference numerals. Again, the meander line 22 is surrounded by a coil 26 of relatively short length. In this case, however, the microstrip conductor 20 is connected to a circulator 33 having a first port 36 for received signals and a second port 38 for transmitted signals and an externally applied direct current magnetic field perpendicular to the ferrite slab. Furthermore, in this case, the Balun circuit 32 is connected to one end of a loop antenna 40, the other end of which is connected to the main section of the microstrip conductor 20.

In the embodiments of the invention shown in FIGS. 2 and 3, the antennas 24 and 40 are formed entirely on one side of the ferrite slab 34 opposite the ground plane. In FIG. 4, an embodiment ofthe invention is shown wherein one-half 42 of a dipole antenna is connected through a Balun loop 44 to a microstrip center conductor 46 deposited on a ferrite slab 48. The other side of the ferrite slab 48 is provided with a ground plane 50 which does not extend entirely to the end of the slab 48. Rather, it is cut away to form the second element 52 of the dipole antenna. Thus, in FIG. 4, opposite halves of the dipole antenna element are on opposite sides of the ferrite slab 48; whereas in the embodiments of FIGS. 2 and 3 they are on the same side and opposite the ground plane.

In FIG. 5, an arrangement is shown similar to that of FIG. 2 and wherein elements corresponding to those of FIG. 2 are identified by like reference numerals. In this case, however, the input end of the ferrite slab 34 is also provided with a dipole antenna 54 provided with a first half 56 connected directly to the center conductor 20 and a second half 58 connected through a Balun loop 60 to the same center conductor 20. This type of phase shifter is particularly adapted for use with a space fed antenna array, such as that shown in FIG. 6. Thus, a plurality of phase shifters 62 each has a ferrite slab 64 projecting outwardly from the rear of encircling coil 66. Each of the outwardly projecting portions 64 of the ferrite slabs is provided with a dipole antenna such as antenna 54 shown in FIG. 5. Thus, when wave energy from a feed horn 68, for example, is directed against the array of dipole antennas 54 at the rear of each phase shifter, it is picked up by each dipole and passes through its associated ferrite phase shifter to the antenna 24 at the forward end of the ferrite slab. A scanning action of the radiated wave energy from the front of the array is obtained by appropriate variation of the phase shift effected by each of the phase shifters in accordance with well known practice.

The details of an antenna array such as that schematically illustrated in FIG. 6 are shown in FIG. 7. Thus, the entire assembly is supported on two plates 66 and 68 which act as a reflector and are connected to the casing 16 (FIG. ll) surrounding each ferrite slab such that the plates 66 and 68, in addition to providing structural strength for the assembly, also act as a heat sink for the heat generated in the ferrite as well as a ground return. All of the coils 66 are connected, on one side, to a common source of 8+ potential via lead 70; while the opposite end of each coil is connected through a transistor driver circuit 72 to a control wire 74 which is, in turn, connected to control circuitry for the antenna array.

Although the invention has been shown in connection with certain specific embodiments, it will be readily apparent to those skilled in the art that various changes in form and arrangement of parts may be made to suit requirements without departing from the spirit and scope of the invention.

Iclaim:

II. A ferrite phase shifter for electromagnetic wave energy comprising a slab of ferrite material having a ground plane deposited on one side thereof and a microstrip conductor deposited on the other side thereof, an electromagnetic coil surrounding said ferrite slab and adapted to produce a longitudinal essentially direct current magnetic field extending parallel to the direction of wave propagation along said microstrip conductor, and microstrips deposited on one end of said ferrite slab and connected to said first-mentioned microstrip to form an antenna element, said antenna element comprising a dipole having a first part connected directly to said microstrip conductor and a second part connected through a Balun loop to said microstrip conductor.

2. The ferrite phase shifter of claim 1 wherein said antenna element comprises a loop antenna.

3. A ferrite phase shifter for electromagnetic wave energy comprising a slab of ferrite material having a ground plane deposited on one side thereof and a microstrip conductor deposited on the other side thereof, an electromagnetic coil surrounding said ferrite slab and adapted to produce a longitudinal essentially direct current magnetic field extending parallel to the direction of wave propagation along said microstrip conductor, microstrips deposited on one end of said ferrite slab and connected to said first-mentioned microstrip to form an antenna element, and other microstrips deposited on the other end of said ferrite slab and connected to said first-mentioned microstrip to form an antenna element, whereby said last-mentioned antenna element is adapted to receive input power which, after passing through the phase shifter, is radiated from the antenna element at the other end of the phase sifter.

4. The ferrite phase shifter of claim 3 wherein each of said antenna elements comprises a dipole having a first part connected directly to said microstrip conductor and a second part connected through a Balun loop to said microstrip conductor.

5. A ferrite phase shifter for electromagnetic wave energy comprising a slab of ferrite material having a ground plane deposited on one side thereof and a microstrip conductor deposited on the other side thereof, an electromagnetic coil surrounding said ferrite slab and adapted to produce a longitudinal essentially direct current magnetic field extending parallel to the direction of wave propagation along said microstrip conductor, and a dipole antenna element deposited as microstrips on one end of said ferrite slab, one part of said dipole antenna element connected through a Balun loop to said firstmentioned microstrip conductor on one side of the ferrite slab and a second part connected to said ground plane on the other side of the ferrite slab, said ground plane terminating at a point removed from said one end of the ferrite slab.

6. A ferrite phase shifter for electromagnetic wave energy comprising a slab of ferrite material having a ground plane deposited on one side thereof and a microstrip conductor deposited on the other side thereof, an electromagnetic coil surrounding said ferrite slab and adapted to produce a longitudinal essentially direct current magnetic field extending parallel to the direction of wave propagation along said microstrip conductor, microstrips deposited on one end of said ferrite siab and connected to said first-mentioned microstrip to form an antenna element, and a circulator on said ferrite slab at the end thereof opposite said antenna element and connected to said microstrip conductor.

7. An antenna array comprising a supporting plate, a plurality of ferrite phase shifters mounted on said supporting plate in two dimensions and spaced apart in an amount equal to one-half wavelength of the wave energy to be radiated from the antenna, each of said phase shifters comprising a slab of ferrite material having deposited thereon a microstrip conductor, an antenna element connected to one end of each of said microstrip conductors, means for coupling wave energy to the other end of said microstrip conductor, a layer of metal deposited on the side of each ferrite slab opposite said microstrip conductor and forming a ground plane, means connecting all of said ground planes to said plate, and electromagnetic coils surrounding all of said ferrite slabs.

8. The antenna array of claim 7 including a second supporting plate and wherein said first-mentioned plate and said second plate are at opposite ends of each phase shifter.

9 The antenna array of claim 7 including a common source of driving potential for all of said phase shifters. 

